Spacer for casting squirrel cage rotors



Aug. 26, 1952 w.' M. EVANS ET AL 2,607,969

SPACER FOR CASTING SQUIRREL CAGE ROTORS Filed Nov. 19. 1948 sSheets-Sheet 1 7P 2pm 5. mam 5e $.32 JNVENTORS BY f4,

. HTTOIQA/E y Aug. 26, 1952 w. M. EVANS ETAL ,5

SPACER FOR CASTING SQUIRREL CAGE ROTORS Filed Nov. 19. 1948 sSheets-Sheet 2 flrroems'x 26, 19 w. M. EVANS ETAL 2,607,969

SPACER FOR CASTING SQUIRREL CAGE ROTORS Filed NOV. 19. 1948 3Sheets-Sheet 5 MILL/44M M. EVfl/VS PHLPH 5'. THRCKEQ IN V EN TOR5UTTOENEV Patented Aug. 26, 1952 UNITED STATES PATENT OF I SPACER FOR GASTING SQUIRREL CAGE ROTORS William M. Evans, La Habra *Heights,and'Ral'ph S. -Tha'cker, Lo's Angeles, Calif., 'assigiiors to U. S.Electrical Motors, Inc., Los Angeles, Calif;, 'a corporation ofCalifornia Ap lication November 19, 194.8,Se'ria1No. 61,092

2 Claims. (01. 22-116) This invention relates to the casting of metal-110 conductors to form a'squirrelc'age of an induction motor rotor.

Rotors of this character are formedof'a stack of laminations havingslots at the periphery for the reception of conductor bars. These barsare joined at their ends by rings of conducting material. v

It is common "to cast snch conductors to form the completed squirrelcage including the end rings, by pouring molten i'netal'into a mold thataccommodates the assembled stack of lamina tions. Copper, aluminum, orother conducting metal may be used; and often the entire mold and thelaminations are rotated to cause the metal to be cast 'centrifugally.

One form of apparatus-for centrifugally casting the squirrel cage isdescribed in Patent 2,381,616, granted August 7, 1-945, t0 George T.Pfleger.

It is often required to provide airvents or duets at intervals along thestack of laminations; these provide passages'for ventilation when themotor is operating, and aids'in maintaining the temperature of the motorat a desired low value.

To ensure that these ventilating ducts will be left intact during thecasting operation, spacers are utilized that can beremoved afterthe-casting is completed. These spacers have a thickness corresponding to thespace to be left between the sections of the stack.

It is one of the objects -"of this invention to provide a spacer-suchthat it can be veryreadily removed after the casting operation iscompleted.

It is another object of this invention generally to improve the processof casting the squirrel cage conductors in the stack of laminations.

In order to maintain the spacing between the sections of thelaminaticns, the 'cast bars are preferably provided with enlargementsoperating as spacers between thes'ections. It is another object of thisinvention to 'providesuch enlargements, the dimensions of whichniay bekeptto close tolerances. In this way, it is assured that theenlargements, while adequate to provide the abutments. yet offer onlyaslightre'sistanc'eto the how of cooling air. Furthermore, theexteriorsurface of the spacerportions can bearranged to provide increasedheatradiating surfaces.

This invention posesses many other advantages, and has other objectswhich'may be made more clearly apparent-froma consideration of severalforms in 'which'it may be embodied. Such forms are shown in the drawingsaccompanying and forming part of thelpresent-s15edification.Thesero'r'mswnrnow bedesc'ribed in de tail, illustrating the generalprinciples of-the invention; but it-is to be understood that suehdetailed description is n'ot'to be takenin a limiting'sense, since thes'cope of the' inventio'n is best defined by theappended claims.

Referrin'g'to the drawing-s:

Figure 1' is aside elevation of a 's'teick 'of laminations utilizing theinvention, and sho'wi-ng'zthe squirrel cage conductors;

Fig.-2 is a pictorial'viewof oneof the spacers utilized in 'connectionwith the casting operation;

Fig. 3 is a sectional'=view,{taken-generally along a surfacecorresponding to tne-1me- 3 s of Fig.1

Fig. 4 15a fragmentary plan viewor tne'spacer shown in Fig.2 I v Fig.51s a fragmentary"sectional"newsman along a plane corresponding to line5-5 of Fig. 3;

Fig. 6 is a sectional view. taken generally-along a plane corresponding-to'line6'-'-6 of Fig.4

Fig. 7 is a view similar to'Fig. 4 of a modified formof the spacerincorporating the invention;

Fig. 8 is an enlarged fragmentary view,'partl'y in section, of thespacer shown'in'Fig. 7;

Fig. 9 is a'view,similar to Fig.-4,-of a further modified form of thespacer;

Fig. 10 is an enlarged sectional view, taken along a plane correspondingto line Hi H) of Fig.9;

Figs. 11 and 12 are views similar to Figs. 4 and 5, and illustratingafurther modified form of the spacer; and V n Figs. 13, 14, and 15 arefragmentary sectional views, similar'to Fig. 3, of modified forms of theinvention. p

In Figs. 1 and'3 there are-illustrated the sections I, 2, 3, 4,5, and Spt laminations comprising the core-of aninduction motor squirrel cagerotor. This core, it is understood, is arranged to be mounted on aspider or a shaft.

One lamination I2 is shown in Fig. 5 and illustrates the slots 1adjacent the'periphery of the lamination. These slots, intl 1'e"-r're's'ent instance, areshow'n as neanymosed, there beingp'ripher r'mrmwslots Bcommiinicatin'g respectively with the slots '1. As shownmostclearlyinFig. 1, the laminations may bes'tacked'in'suchrnanher thatthe squirrel csgeeondu ctors intheslots are oblique to the axis,"producing "the desired skew' arrangement. k I

Cast within the slots"! and fi'arethe squirrel cage bars '9. These barsare integrally J'Qined with the endrings Mandi l. rneseend rings ma-carry the rim blades l ram [5.

In order to cast the bars 9 and the end rings Ill and II as a unit andto form the air spaces between the stacks of laminations, use is made ofspacers 16 that are disposed between the sections of the stack and thatmay readily be disintegrated afterthe casting operation is completed.Thesespacers'are shown in Figs. 1 and 3; but, since the bars 9 and theend rings l and II have already been cast, these spacers are to beremoved in order to complete the manufacture of the rotor.

To prepare the laminations for the casting operation, they are carefullystacked with the slots 1 and 8 of the laminations properly aligned. Asshown in Figs. 1 and 3, the sections l to 6 inclusive are spaced apartby the spaced rings IS. The complete stack is clamped in properassembled relation, and then the entire stack assembly is preheated at atemperature neighboring l100- F. The assembly is then transferred to acasting mold which may be made of metal, and the mold is rotated duringthe process of casting. Molten metal, such as aluminum or copper, isthen poured intqthe revolving mold.

The cast rotor maythen. be removed from the mold for proper machining ofthe cast metal bars and end rings However, before this is accomplished,the spacer rings iii are removed, forming the vents or ducts between thesections of the laminations.

In order that these spacer rings l6 may be readily disintegrated, theyare made from a special plaster materiaL-or plaster composition, which,uponthe application of heat, changes its characteristics and willdisintegrate upon contact with water. The disintegrated spacers may thenbe completely removed by washing or brushing as, for example, by astream of water flowing from anozzle; V 7

Plaster compositions capable of being thus disintegrated include gypsumand crystobalite. The composition is in the form ,of a fine powder. Whenheat is applied to a casting of this material, it expands, anddisintegrates readily when plunged into Water. a

Since the plaster material is quite brittle; provisions are made forreinforcingthese plaster spacers. This is essential because of thehandling of these spacers; after they are once in the stack, they areproperly maintained in place by the reinforcing effect-of the adjacentsections. In the form shown in Figs. 2, 4, and 6, metal reinforcingwires I! may be embedded in the plaster composition near the peripherythereof. Furthermore, in this instance, the slots I8 of the spacer areshown as skewed (Fig. 6) to correspond with the skew formation of theslots defined by the laminated stack. These slots may be entirely closedto provide additional strength. They may be made somewhat larger thanslots 1 of the laminationaso as to overlap them. In this way theyprovide for the formation of the enlarged portions [3 ofthe bars 9.Furthermore, in order to assist in aligning the slots 18 of the spacerIS with the slots 1, marks in the form of small depressions l9 (Fig. 4)may be provided on the outer periphery of the spacer [6,

The enlarged ends 13 can be precisely cast, and their "dimensions aremaintained with small tolerances, because the plaster spacers [6 are notaffected by the high temperatures during the casting operations. Sharpand smooth surfaces are therefore formed on. these enlargements, andthere is no dangerthat the metal'willflow, so as 1 to block the air ductsubstantially entirely. A free flow of cooling air is maintained.

The forms of the bars between the sections I to 6 may be difierent. InFig. 13, the enlarged parts 36 are substantially spherical. In Fig. 14,the enlargements are in the form of narrow flanges 31; andin Fig. 15,corrugations 38 are formed to increase the radiation of heat while themotor is in operation.

These forms are merely examples capable of being produced by appropriateshaping of discs I6.

The plaster discs or spacers l6 are conveniently formed by a moldingoperation. A master mold of plastic material, such as a rubber mold, canbe formed by pouring the molten plastic material over a master patterncorresponding to the disc I6. The molten plastic, when it cools, issumciently flexible so that it can be stripped from the master pattern.This plastic mold can then be used for the casting of the plaster discsor spacers l6. r I V The material used for casting these discs, asheretofore stated, is a plaster mixture, preferably includingcristobalite, having an ingredient that permits the plaster material tobe readily disintegrated in water. i 1

The plaster discs-or spacers [6 are preferably coated on each side witha graphite and oil mixture. In this way leakage or flash of the moltenmetal at the joint between the spacer-and the laminations is prevented.When the plaster spacers I6 are removed from the stack, as shown in Fig.3, the enlarged portions [3 of the bars 9 are recessed below the outerperiphery of the rotor. The effect of this is to reduce windage noisewhile the motor is operating.

The spacers [6, being made from brittle cast plaster material, must becarefully handled when assembling the stack of laminations. Just as soonas the stack is completed with the spacers interposed between thesections of laminations, it is not important to keep the plaster discsfrom cracking. In order to ensure that the plaster discs can be handledwithout premature cracking or breaking, the reinforcements I! areprovided.

After the molding operation is completed, the entire rotor is immersedin water, and the plaster spacers are removed.

Other forms or reinforcements may be used.

In the form shown in Figs. 7 and 8, the plaster spacer '20 is shown ashaving the open slots 2! and a reinforcing band 22 of metal at theoutside periphery. This band of metal is so arranged that it presents noradial protuberances. Thus, where the edges 23 and 24 overlap, they arearranged to form a substantially continuous circular form. Furthermore,if desired, the metal band 22 can be attached to the plaster disc as byappropriate fastening means, such as the nails 25. These nails 25 arecast into the plaster between the slots 2!. Recesses are formed in theband '22 to accommodate the heads of these nails.

In the form shown in Figs. 9 :and 10, reinforcement is provided by theaid of either the outer band 26 or the inn-er band 27, or both. In thiscase these bands may be formed of thin micarta, or equivalent materials.As shown most clearly in Fig. '10, apertures 28 in the bands may providefor the keying in of the plaster disc 29. The micarta bands are thuskeyed firmly in place.

Duringthe step of preliminary heating the assembled stack utilizing themicar-ta reinforced r ngs or spacers 29, these micarta bands 26 and areburned away, leaving merely the plaster discs 29. These, in turn, arereadily disintegrated by the aid of Water after the casting operation.

In the form shown in Figs. 11 and 12, metal bands 30 and 31 on the innerand outer peripheries of the plaster spacer 32 are utilized. Here themetal bands are held in place by the nails 33 and 34, embedded when thespacers 32 are molded. The heads of these nails are appropriatelyrecessed within the bands.

After the plaster materials are disintegrated, the reinforcing metallicelements, such as the nails 33 and 34 and the bands 30 and 32, areeasily removed from the completed rotor.

The inventors claim:

1. A spacer for use between sections of laminations of a dynamo-electricmachine for providing ventilating spaces in the stack of laminations,said spacer being made from a composition of gypsum and cristobalite.

2. A spacer for use between sections of laminations of a dynamo-electricmachine for providing ventilating spaces in the stack of laminations,said spacer being made from a composition of gypsum and cristobalite,and having a general WILLIAM M. EVANS. RALPH S. THACKER.

REFERENCES CITED The following references are of record in the file ofthis patent:

UNITED STATES PATENTS Number Name Date 371,176 Coleman Oct. 11, 1887481,295 Black 'Aug. 23, 1892 976,465 Hunty Nov. 22, 1919 1,932,292Coleman et al. Oct. 24, 1933 2,163,373 Cooper June 20, 1939 2,313,672Salzberg Mar. 9, 1943 2,352,083 Detjen June 20, 1944 2,968,296 GoranJan. 30, 1945 2,369,067 Mayer Feb. 6, 1945 2,474,186 Marks June 21, 19492,594,823 George Apr. "18, 1950

1. A SPACER FOR USE BETWEEN SECTIONS OF LAMINATIONS OF A DYNAMO-ELECTRICMACHINE FOR PROVIDING VENTILATING SPACES IN THE STACK OF LAMINATIONS,SAID SPACER BEING MADE FROM A COMPOSTION OF GYPSUM AND CRISTOBALITE.